Certain facilities, such as large data processing centers, require a continuous supply of power. In order to assure a continuous supply of power, these facilities rely upon an auxiliary or backup power system, such as an uninterruptible power system (UPS). In addition to the UPS, one or more internal combustion engine-driven generators may be utilized for UPS support during extended power outages. Typically, a facility depends upon the public utility to provide for its day-to-day power demands. The UPS provides continuous power to feed the critical loads through a system generally comprising a rectifier, batteries and inverter. Upon the occurrence of a power failure at the public utility, the batteries serve as a power source for a very short duration, a maximum of fifteen minutes, typically. This allows the engine/generator time to come on line and to take over as the substitute power source until power from the public utility is restored. In the cases where an engine/generator is not part of the power system, or fails to come on line, the batteries supply enough power to allow the facility or the data processing center to execute an orderly shut down procedure so that them will be no loss or a minimal loss of information.
The proper functioning of the backup power system is critical. The backup power system must always be in a state of readiness to take over the power supply function from the public utility. However, in some cases, little or no attention is paid to the operational readiness status of the backup system, despite its critical function. The neglect of the backup system can result in the complete loss of power during a public utility power outage. The consequent dangers include irretrievable loss of data if a computer system depends upon the backup system for power delivery. Further, in some facilities, such as hospitals, the failure of the backup system can result in serious personal injury or death.
Periodic testing of the backup power system is a requisite for those facilities which require a continuous source of power. Further, whenever the load that the facility puts on the power system is changed, especially when the load is increased, the backup power system must be tested in order to determine whether the backup system can handle the changed load. However, testing a backup power system poses several problems. A test which simply switches the facility's on-line load to the backup system to see if it can handle the load is not always desirable. Such a test could prove disastrous if the backup system is not functioning properly or if it is inadequate for the load. Also, disconnecting the backup system in order to conduct testing is not usually a feasible option as the facility would not have a substitute for the public utility power in the case of a power outage during testing. Thus, testing of the backup facility must be done on-site, without interrupting the commercial power supply to the facility, and without disconnecting the backup system from the facility.
The proper testing of a backup power system includes testing all major functions of the backup system and testing such functions in a way so as to duplicate the anticipated load as accurately as possible. In a backup power system comprising an engine/generator and UPS/battery set, both parts of the system must be tested. Prior art testing devices typically only test the battery set of a backup system. Generally, prior art devices use conventional battery testers to test each separate cell of the batteries. Such individual cell testing does not adequately test cell connections under load conditions, does not adequately assess the performance of the battery set as a unit, and does not provide comprehensive testing of the complete backup power system.
Further, to properly test the engine/generator system it must be evaluated with a test load simulating the load which the backup system would have to service in the case of a power outage. Generally, the load to be serviced is a nonlinear and/or reactive load. However, prior art testing devices typically test backup power systems with a simple unity power factor resistive load. This type of testing is inadequate to determine whether a backup system will function properly when servicing the actual, nonlinear and/or reactive load in an emergency situation.
Further, prior art testing devices have been complicated, specialized devices which require highly skilled personnel for their administration. Testing the backup system has been a burden to the serviced facility in that such testing diverts already strained personnel resources and requires the skill of highly trained individuals to set up and administer the test. Often, where the facility is in continuous operation, there is no time which is convenient for testing the backup system. As a result of these problems, most backup power systems are rarely tested, or inadequately tested, and often, tested only through the actual occurrence of an emergency. provided load current signals and load voltage signals, the controller provides first control signals to the rectifier and second control signals to the load bank. The rectifier is connected to the AC power source. In response to the first control signals from the controller, the rectifier simulates a first set of load characteristics by rectifying power provided by the AC power source at a selectable point on the AC waveform. In the preferred embodiment, the rectifier simulates predetermined non-linear load characteristics. In another embodiment, the rectifier simulates predetermined reactive load characteristics. The rectifier comprises a thyristor group in the preferred embodiment. The load bank is connected to the rectifier. In response to the second control signals from the controller, the load bank simulates a second set of load characteristics. In the preferred embodiment, the load bank simulates predetermined linear load characteristics. In one embodiment, the load bank comprises a first load group. In the preferred embodiment, the load bank comprises a first load group, and a second load group connected in parallel with the first load group.
The present invention also provides a method for testing an AC power source by simulating a load with desired characteristics comprising the steps of: providing first control signals and second control signals in response to current signals, load voltage signals and user input signals, where the user input signals correspond to the desired characteristics of the load; simulating a first set of load characteristics by rectifying power provided by the AC power source at selected points on the AC waveform in response to the first control signals; simulating a second set of load characteristics by a load bank in response to the second control signals; providing load current signals in response to the current drawn by the load bank; and providing load voltage signals in response to the voltage across the load bank. In the preferred embodiment, the step of simulating the first set of load
Thus, there is a need in the art for a method and an apparatus to completely and accurately test the load capability of a backup power system comprising an engine/generator and a UPS, including a set of batteries.
Further, there is a need in the art for a method and an apparatus to test the backup power system with a load that simulates the load of the serviced facility.
In particular, there is a need in the art for a method and an apparatus to test the backup power system with a nonlinear and/or reactive load which simulates the load which would be actually carried by the power system.
There is also a need in the art for a means to test the battery set of a backup power system under load conditions by testing the battery set as a unit under constant kilowatt load conditions.
In addition, there is a need in the art for a method and an apparatus to test the backup power system quickly, conveniently and without disrupting the operations of the facility served by the backup power system.